302 BULLETIN 76, UNITED STATES NATIONAL MUSEUM. 



HENRICIA POLYACANTHA Fisher. 

 PI. 78, figs. 1, 4; pi. Ill, figs. 2, 2a-h. 



Eenrida polyacantha FisHER,-Proc. Wiwh. Acad. Sci., vol. 8, Aug.fl4, 1906, p. 129. 



Diagnosis.— Rays moderately slender (R = about 6 r), very flexible, tapering 

 gradually to bluntly pointed, upturned tip; abactinal surface usually more or less 

 collapsed; abactinal and lateral surfaces Avitli small evenly spaced paxillag; single 

 large pajnilic arranged in fairly regular oblique transverse series on either side of 

 median radial line (at least when viewed internally); very small marginal plates; 

 a very regular series of inframarginal papulae; adambulacral spinelets very numer- 

 ous, and on the furrow face of plate two to six small saber-shaped spinelets. 



Description. — Rays, five. R = 66 mm.; r = ll mm.; R = 6 r. Breadth of ray 

 at base, 13 mm. Abactinal and lateral surfaces closely covered with small, unequal 

 pseudopaxilliv, leaving, however, papular areas considerably larger than the plates; 

 papuliB, one to an area, large. Without aid of a glass the papular areas appear 

 roundish. Paxillse more or less elongated in one direction; convex, covered with 

 exceedingly small spinelets, which are numerous, but vary greatly in number, 

 according to the size of pseudopaxilla; ten to forty is the usual number. Paxillse 

 form a more or less evident median radial line along ray. Frequently two rows of 

 pseudopaxillte intervene between two papular areas or pores. 



External to adambulacral plates is a regular series of actinal intermediate 

 plates, and separated from the latter by a conspicuous regular series of papulae is 

 a row of smaller inferomarginals. Separating the regular papulae of this series is a 

 second row of small transversely oriented compressed plates wliich do not extend 

 the whole length of ray. There is considerable variation in this character; the 

 marginal plates are often quite irregular. Sometimes a superomarginal series can 

 be distinguished just above the inferomarginals, especially on outer part of ray, 

 where the two series are fairly regular. At base of ray the serial arrangement is 

 broken up and two or three additional series of small intermarginal plates are 

 interpolated, a single series of very small ones extending far along ray. 



Adambulacral plates separated by a distinct suture. Armature very dense, 

 consisting of many spinelets, as follows: (1) on furrow face of plat.es two to six 

 small saber-shaped spinelets in a vertical series or group. The number varies in 

 different individuals. Usually there are four to six at base of ray and two or three 

 to each plate beyond middle. Rarely specunens have more than three on jilates of 

 distal portion of arm. (2) On actinal surface of plate are thirty to forty slender 

 pointed spinelets arranged in three or four transverse series on inner half of plate, 

 but too crowded on outer half to form rows. Even the inner spinelets are often 

 without regularity. Spinelets decrease rapidly in length and cahber from the 

 furrow outward, the outer spinelets being sharper than the inner and about the 

 same size as those on other actinal plates. 



Mouth plates small, triangular, with about four to seven small p!i])illiform 

 spinelets on furrow face. The actinal surface is densely covered with spinelets. of 

 which eight or nine stand on the free martrin. 



